System and method for geographically locating a cellular phone

ABSTRACT

According to an embodiment of the invention, there is disclosed a method for geographically locating a cellular phone. The method comprises: determining an effective cell-area for each of a first cell and a second cell in a cellular network; and determining a handover area within which the cellular phone is likely to be located when control of the cellular phone is transferred from the first cell to the second cell; wherein the determination of the handover area and the effective cell-area for each of the first cell and the second cell are made based on a topological relationship between the first cell and the second cell. Further related apparatus embodiments are also disclosed.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/888,631 filed 9 Jul. 2004, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

This invention relates to systems and methods for geographicallylocating a cellular phone; and in particular to the use of such systemsand methods for locating vehicles in a traffic information system

BACKGROUND

Determining the geographical location of a cellular phone is useful in avariety of applications, including applications in the field oflocation-based services. In traffic information systems, for example,the locations of vehicles may be determined based on the locations ofdrivers' cellular phones, in order to form an image of trafficconditions. The location of a cellular phone can be determined based ondata acquired from the cellular network itself. In particular, thelocation can be specified in terms of the network cell in which thecellular phone is located, as defined by a cell-identifier, possibly inaddition to other data such as a time-advance.

There is an ongoing need, however, for accurate techniques ofdetermining the geographical location of cellular phones, in manyapplications.

SUMMARY

According to an aspect of the present invention there is provided amethod for geographically locating a cellular phone, the methodcomprising determining an effective cell area for each of a first celland a second cell in a cellular network and determining a handover areawithin which the cellular phone is likely to be located when control ofthe cellular phone is transferred from the first cell to the secondcell. The determination of the handover area and the effective cell-areafor each of the first cell and the second cell are made based on atopological relationship between the first cell and the second cell.

According to another aspect of the present invention, there is provideda method for geographically locating a cellular phone in a cellularnetwork comprising a first antenna for a first cell and a second antennafor a second cell, the method comprising (i) determining an effectiveradius R_(i) for each of a set of i different topological relationshipsbetween the first cell and the second cell, (ii) determining an angle afor which, when the first antenna is contained within the second cell,and when an angle β formed by a line between the first antenna and thesecond antenna and a sector limit line of the second cell is less thanthe angle α; the second cell will be extended beyond the sector limitline, (iii) determining a first extension width E₁ of a firstrectangular extension added to a sector limit line of the second cellwhen the angle β is less than the angle α; (iv) determining a secondextension width E₂ of a second rectangular extension added to a sectorlimit line of the second cell when the first antenna is outside thesecond cell, and when an inner angle formed between a sector limit lineof the second cell and a line between the first antenna and the secondantenna, is greater than 180 degrees, (v) determining a first penumbrawidth W₁ of a first rectangular strip between a line of equal intensityof signal reception from the first antenna and the second antenna, and afirst strip limit proximal to a cell into which the cellular phone ismoving, (vi) determining a second penumbra width W₂ of a secondrectangular strip between the line of equal intensity and a second striplimit proximal to a cell out of which the cellular phone is moving, and(vii) determining a handover area within which the cellular phone islikely to be located when control of the cellular phone is transferredfrom the first cell to the second cell, the determination of thehandover area being based on at least a subset of the effective radiiR_(i), the angle α; the first extension width E₁, the second extensionwidth E₂, the first penumbra width W₁, and the second penumbra width W₂.

According to another aspect of the present invention, there is provideda method of geographically locating a cellular phone by determining thearea in which handover from a first cell to a second cell occurs, themethod comprising modeling at least a portion of a cell reception areaof said first cell and said second cell and defining a handover areacomprising overlapping portions of said first and second cell areas.

According to another aspect of the present invention, there is provideda method of monitoring traffic flow by determining successive locationsof a plurality of cellular phones located in a plurality of vehicles,the method comprising repeat determination of the location of at leastsome of the plurality of cellular phones. This determination ispreferably by means of sampling the locations of the at least some ofthe cellular phones to determine a present picture of traffic flow. Thestep of determining the location of a cellular phone of the pluralitycomprises determining the area in which handover from a first cell to asecond cell occurs, the handover determination being based on modelingat least a portion of a cell reception area of said first cell and saidsecond cell and defining the handover area to comprise overlappingportions of said first and second cell areas.

According to another aspect of the present invention, there is providedapparatus for geographically locating a cellular phone, the apparatuscomprising an effective cell-area module for determining an effectivecell-area for each of a first cell and a second cell in a cellularnetwork and a handover area module for determining a handover areawithin which the cellular phone is likely to be located when control ofthe cellular phone is transferred from the first cell to the secondcell. The determination of the handover area and the effective cell-areafor each of the first cell and the second cell are made based on atopological relationship between the first cell and the second cell.

According to another aspect of the present invention, there is providedapparatus for geographically locating a cellular phone by determiningthe area in which handover from a first cell to a second cell occurs,the apparatus comprising an effective cell-area module for modeling atleast a portion of a cell reception area of said first cell and saidsecond cell, and a handover area module for defining a handover areacomprising overlapping portions of said first and second cell areas.

According to another aspect of the present invention, there is providedapparatus for monitoring traffic flow by determining successivelocations of a plurality of cellular phones located in a plurality ofvehicles. The apparatus comprises (i) a handover area module fordefining a handover area comprising overlapping portions of a modeledcell reception area of at least a portion of each of a first cell and asecond cell of a cellular network, and (ii) a sampler module forsampling a set of repeated location determinations of at least some ofthe plurality of cellular phones, to determine a present picture oftraffic flow, wherein each such location determination is based at leastin part on the handover area defined by the handover area module for agiven cellular phone moving between a given first cell and second cellof the cellular network.

Additional advantages and novel features of the invention will be setforth in part in the description which follows, and in part will becomeapparent to those skilled in the art upon examination of the followingand the accompanying drawings; or may be learned by practice of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how thesame may be carried into effect, reference will now be made, by way ofexample only, to the accompanying drawings, in which:

FIG. 1 shows first and second cells of a cellular network havingantennas located at the same point, in accordance with an embodiment ofthe invention;

FIG. 2 shows first and second cells of a cellular network, the cellshaving antennas located at different points, and oriented to face eachother, in accordance with an embodiment of the invention;

FIG. 3 shows first and second cells of a cellular network, the cellshaving antennas located at different points, and having sectors that donot overlap, in accordance with an embodiment of the invention;

FIG. 4 shows first and second cells of a cellular network, the cellshaving antennas located at different points, which face at an acuteangle to each other, and whose sectors overlap, in accordance with anembodiment of the invention;

FIG. 5 shows an effective cell-area with extensions of a sector when oneantenna is contained in the sector of another cell, near one of itslimiting lines, in accordance with an embodiment of the invention;

FIG. 6A shows an effective cell-area with extensions of a sector when asecond antenna is outside the limits of the sector of a first antenna,and when an inner-angle criterion is satisfied for two edges of thesector, in accordance with an embodiment of the invention;

FIG. 6B shows an effective cell-area with extensions of a sector when asecond antenna is outside the limits of the sector of a first antenna,and when an inner-angle criterion is satisfied for one edge of thesector, in accordance with an embodiment of the invention;

FIG. 7 illustrates the determination of a penumbra area around the lineof equal intensity between two antennas, in the case in which two cellshave antennas located at the same point, in accordance with anembodiment of the invention;

FIG. 8 illustrates the determination of a penumbra area around the lineof equal intensity between two antennas, in the case in which two cellshave antennas located at different points, and are oriented to face eachother, in accordance with an embodiment of the invention;

FIG. 9 illustrates the determination of a handover area for the case inwhich two cells have antennas located at different points, and areoriented to face each other, in accordance with an embodiment of theinvention;

FIG. 10 illustrates the determination of a handover area for the case inwhich a line of equal intensity is not well-defined, in accordance withan embodiment of the invention;

FIG. 11 shows a ring-sector, which is used to model the estimatedlocation of a cellular phone when a cellular network uses time advancedata, in accordance with an embodiment of the invention;

FIG. 12 is a block diagram of a traffic information system, as part ofwhich an embodiment according to the invention may be used; and

FIG. 13 is a block diagram of an apparatus for locating cellular phones,in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Although techniques are known for determining the location of a cellularphone based on the network cell in which the phone is located, theaccuracy of such techniques is limited by the large geographical areacovered by each cell. Other techniques are known in which a specificmachine is used to actively monitor the location of given handsets byrequest. However, such techniques load the network, and are thereforecostly and limited in capacity.

Cellular networks operate using a network of antennas, each of whichcommunicates messages to and from cellular phones located in a givenarea, called a cell. Cell areas from different antennas overlap, so thatthe domain of operation of the cellular network is completely covered.At any given time, a cellular phone is under the control of a singlecell of the network. The controlling cell is usually the one whosereception intensity is the strongest at the location of the cellularphone. When a cellular phone is in motion, it traverses from cell tocell, and its control is “handed over” from one cell to another. Theevent of control transfer from cell to cell is called “handover.”

Theoretically, a handover event from cell A to cell B occurs when acellular phone moves from an area where the intensity of the signal fromthe cell A antenna is higher than that of the cell B antenna, to an areawhere the intensity of the signal from the cell B antenna is higher thanthat of the cell A antenna. Thus, the handover event shouldtheoretically occur when the cellular phone crosses a line ofequal-intensity signals from both cells. However, in reality, thehandover does not occur exactly on the equal-intensity line, but ratherwithin a certain penumbra area around the equal-intensity line. The formand dimension of the penumbra area depends on various parameters,including the relative positioning of the cells involved, which isdetermined by the location and orientation of the antennas.

In an embodiment according to the invention, there is disclosed atechnique for geographically locating a cellular phone with highconfidence at the moment that handover occurs, by determining the“handover area,” which is the area in which handover from cell A to cellB might occur at high probability. Because the handover areas are foundto be smaller than cell areas, on average, this technique offers betteraccuracy than techniques that use only the cell area to locate a phone.Additionally, handover events are recorded by the cellular networkmanagement system, and are therefore available at no additional cost, sothat the technique is relatively inexpensive.

In order to implement an embodiment according to the invention, apolygon must be constructed to represent the handover area. In order todo so, four simplifying assumptions are made.

First, the simplifying assumption is made that the control area of anantenna (a cell area) is a sector, generally of 120 degrees, whosecenter is the antenna; see, for example, sector 101, centered aroundantenna 100 of the embodiment of FIG. 1.

Second, the simplifying assumption is made that the reception intensityof signals from the antenna grows in inverse relation to the distancefrom the antenna, while the cellular phone is located within the sector.Other factors that influence the reception intensity of signals from theantenna are ignored, such as the exact azimuth of the antenna, theeffect of reflections, and the effect of multi-pathing; because theinfluence of such factors is limited, and the factors oftenstatistically offset one another.

Third, the simplifying assumption is made that the reception intensityfrom the antenna outside the sector is significantly lower than thereception intensity within the sector.

Fourth, the simplifying assumption is made that the handover from onecell to another occurs within a reasonable distance from a point wherethe cellular phone receives a signal from both antennas at equalintensity.

Based on these assumptions, an embodiment according to the inventioninitially models a cell's reception area as a sector with a finalradius. Beyond that radius, reception does occur, but it issignificantly weaker than reception within the radius. Also, there areregions of weak reception beyond the limiting lines of the sector; andin the area behind the antenna, in the opposite direction from thesector. In some cases, control over a cellular phone can be handed overwithin these weak reception areas. An embodiment according to theinvention therefore extends the cell reception area, initially modeledas a sector, into these weak reception areas, in certain circumstances.Once the effect of such circumstances has been considered, and the cellsector area possibly extended (or not), the resulting model of thecell's reception is here termed the effective cell area. As will be seenfurther below, whether to extend a cell sector area can be determinedbased on the relative positions and orientations of the two antennasbetween which a phone is moving. For example, extensions can be madewhen one cell's antenna is situated within the other cell's sector, butvery close to the sector's limit (as in the embodiment of FIG. 5); orwhen one cell's antenna is situated outside the other cell's sector inspecific configurations (as in the embodiment of FIG. 6). In thesecases, the effective cell area includes extensions beyond the sectorlimits. Also, the radius of the sector can be extended or diminished, insome cases, based on the distance between the antennas of the two cells;the resulting radius is here termed the effective radius of the cell.

By taking such effects into consideration, an embodiment according tothe invention constructs a polygon representing the handover area out ofa combination of two areas: 1) the overlap part of the effectivecell-areas of the two cells between which the cellular phone is moving;and 2) the penumbra area around the equal-intensity line between theantennas of the two cells. As will be seen below, the relativepositioning of the two cells plays a significant role in thedetermination of these two areas; and there are cases in which thepenumbra area is impossible to define, and therefore only the effectivecell area is used.

FIGS. 1 through 4 illustrate four possible topological relativepositions of two cells, in accordance with an embodiment of theinvention. In FIG. 1, a first cell 101 and a second cell 102 haveantennas located at the same point 100. In FIG. 2, a first cell 201produced by a first antenna 203 is oriented to face a second cell 202,produced by a second antenna 204; the two cells have antennas located atdifferent points, and are facing each other. In FIG. 3, a first cell 301and a second cell 302 have antennas 303 and 304 located at differentpoints, and their sectors do not overlap. FIG. 4 shows an example whichdoes not fit into the topological categories of FIGS. 1 through 3,thereby representing all other topological cases; in this case, antennas403 and 404 are located at different sites, are facing at an acute angleto each other, and the sectors 401 and 402 overlap.

In an embodiment according to the invention, a method for geographicallylocating a cellular phone includes three steps: first, determining theeffective cell-area of each cell; second, determining the penumbra areaaround the equal-intensity line; and third, combining the areasdetermined in the first and second steps to determine the handover area.

A first step of an embodiment according to the invention comprisesdetermining the effective cell-area of each cell. In order to do so,there is first determined an effective radius of the cell-sector. Theexistence of such a radius is premised on the second simplifyingassumption above, i.e. that the reception intensity of the antennawithin the sector grows in inverse relation to the distance from theantenna. Determining the effective radius depends on the topologicalcase involved: in the topology of the embodiment of FIG. 1, in which theantennas are located at the same site 100, the effective radius isR_(i), 103. in all other topological cases, shown in the embodiments ofFIGS. 2 through 4, the effective radius is equal to R_(i)*D, where D isthe distance between the antennas, and R_(i) is a constant factor,different for each topological case (i.e. for FIGS. 2 through 4, theindex i=2, 3, and 4). In accordance with an embodiment of the invention,other methods for determining an effective radius may be used; includingother methods that relate an increased distance between the antennas toan increased effective radius.

Next, after determining the effective radius of the cell-sector, theeffective cell-area is determined by extending the cell sector beyondthe edges of the sector, in certain cases. This determines the sidelinesof the effective cell-area. The extension of the cell-area beyond theedges of the sector is required in two cases: 1) when one antenna iscontained in the sector of the other cell, very near one of its limitinglines, as will be illustrated with reference to the embodiment of FIG.5; and 2) when one antenna is outside the sector of the other cell, andthe inner angle between the limiting line and the line connecting bothantennas is greater than 180 degrees, as will be illustrated withreference to the embodiments of FIGS. 6A and 6B.

In the first extension case, shown in the embodiment of FIG. 5, theangle β, 503 that is formed by the line 505 between the two antennas 501and 502, and one of the limiting lines 506 of the first sector, is lessthan a pre-determined angle α 504. The predetermined angle α ispre-determined as the angle within which an antenna 502 is sufficientlyclose to the limiting line 506 to warrant an extension of the cell-areabeyond the edges of the sector. When the angle β is less than α, thesector is extended only to one side, i.e. the side 506 that is near tothe second antenna 502. A relatively small rectangular extension 508,which has a width dimension E₁, 507, is added to the side 506 of thesector.

In the second extension case, described first with reference to theembodiment of FIG. 6A, a second antenna 602 is outside the limits of thesector 603 of a first antenna 601. In such a case, it is determinedwhether the inner angle, i.e. the angle that contains the first sector603 itself, and that is formed between an edge 607 or 608 of the sector603 and the line 609 between the two antennas 601 and 602, is greaterthan 180 degrees. If so, an extension is made to the sector edge 607 or608 for which that condition is satisfied. For example, consider edge607 of the sector 603. The inner angle between edge 607 and the line 609is angle 605; and that angle 605 is greater than 180 degrees.Accordingly, edge 607 is extended by a rectangular extension 610.Similarly, considering edge 608 of the sector 603, the inner anglebetween edge 608 and the line 609 is angle 606; and that angle 606 isgreater than 180 degrees. Accordingly, edge 608 is extended by arectangular extension 611. In the second extension case of FIGS. 6A and6B, the rectangular extensions, such as extensions 610 and 611, have arelatively larger width E₂, 613 than the width E₁, 507 of therectangular extension of FIG. 5. Also, when there are two rectangularextensions to a given sector, as with extensions 610 and 611 on sector603, an additional triangular extension 612 is made at the back ofantenna 601 by connecting the two far corners 623 and 624 of therectangular extensions; and the two extensions are of the same width E₂.It should be noted that, whereas large extensions are made to sector 603because antenna 602 is outside the limits of the sector of antenna 601(and the inner-angle criterion is satisfied), the reverse is notnecessarily the case for the other sector. That is, in this case, sector604 will not be extended by an extension of the second type, becauseantenna 601 is within sector 604.

The embodiment of FIG. 6B shows another example of an extension of thesecond type, in which only one edge of a sector is extended with a largeextension, instead of two. In particular, antenna 615 is outside thesector 616 of antenna 614. However, the inner angle 622 between sectoredge 617 and the line 620 is exactly equal to 180 degrees (and thereforeis not greater than 180 degrees), so that no extension is made to edge617. By contrast, the inner angle 621 between sector edge 618 and theline 620 is greater than 180 degrees; therefore, an extension 619 of thesecond type is made to edge 618.

Having determined the effective cell-area (by determining an effectiveradius and, in some cases, extending the edges of the sector), thesecond step of an embodiment according to the invention is to determinethe penumbra area around the line of equal intensity between the twoantennas, as illustrated with reference to the embodiments of FIGS. 7and 8. The penumbra area around the line of equal intensity is modeledas an asymmetrical rectangular strip around the line of equal intensity.The width W₁ of the rectangular strip between the line of equalintensity and the strip limit on the side of the cell into which thecellular phone is moving, is longer than the width W₂ on the side of thecell out of which the cellular phone is moving. For example, withreference to the embodiment of FIG. 7, the penumbra area around the lineof equal intensity 710 is formed by two rectangular strips 706 and 707,for which the width W₁, 708 of the strip 706 on the side of the sector704 into which the cellular phone is moving, is longer than the widthW₂, 709 of the strip 707 on the side of the sector 705 out of which thecellular phone is moving. Each strip is formed between the line of equalintensity 710 and a strip limit 711 and 712. Similarly, with referenceto the embodiment of FIG. 8, the penumbra area around the line of equalintensity 808 is formed by two rectangular strips 806 and 807, for whichthe width W₁, 809 of the strip 806 on the side of the sector 805 intowhich the cellular phone is moving, is longer than the width W₂, 810 onthe side of the sector 804 out of which the cellular phone is moving.

In determining the penumbra area around the equal intensity line,according to an embodiment of the invention, it is first necessary todetermine the location of the equal intensity line, which variesdepending on the topological case. In the first topological case of theembodiment of FIG. 1, which is also the case in FIG. 7, the equalintensity line is the bisector 710 of the cells' azimuths 702 and 703(which emanate from the location 701 of the antennas). In the second andthird topological cases of the embodiments of FIGS. 2 and 3, the equalintensity line is approximately the central perpendicular to the lineconnecting the two antennas. For example, in FIG. 8, which correspondsto the topological case of FIG. 2, the equal intensity line is thecentral perpendicular 808 to the line 803 connecting the two antennas801 and 802. In the fourth topological case of the embodiment of FIG. 4,the equal intensity points are difficult to define, and a strip similarto those of FIGS. 7 and 8 does not exist.

Having determined the effective cell-area and the penumbra area aroundthe line of equal intensity, a third step of an embodiment according tothe invention is to determine the handover area. For each of thetopological cases except that of the embodiment of FIG. 4, the area inwhich each cell is potentially able to perform a handover is formed, foreach cell, by the intersection of its effective cell-area and thepenumbra area around the line of equal intensity. The cell A to cell Bhandover area is then found as the union of the areas in which the twocells are potentially able to perform a handover. For example, withreference to the embodiment of FIG. 9, the handover area for a cellularphone traveling from cell A, 901 to cell B, 902 is determined by firstintersecting the effective area of cell A with the rectangular strip 903of the penumbra area around the equal intensity line 904; thenintersecting the effective area of cell B with the rectangular strip903; and then forming union of these two areas, which is represented asthe shaded area 905. The embodiment of FIG. 9 illustrates thedetermination of the cell A to cell B handover area for the topologicalcase of the embodiment of FIG. 2, in which the rectangular strip 903 iswell defined. In the topological case of the embodiment of FIG. 4, forwhich a similar rectangular strip is not defined, the cell A to cell Bhandover area is found as the intersection of the two effectivecell-areas, each of which may include extensions of either the first orsecond type described above. For example, in the embodiment of FIG. 10,the effective cell-area of sector 1001 has been extended by an extension1002 of the first type, and the effective cell-area of sector 1003 hasbeen extended by extensions 1004, 1005, and 1006 of the second type.Because this is a topological case similar to that of the embodiment ofFIG. 4, the handover area from cell 1001 to cell 1003 is equal to theintersection between their two effective cell-areas, which is shown asshaded area 1007. It should be noted that the only difference between acell A to cell B handover area, and a cell B to cell A handover area,derives from the asymmetry of the penumbra area around the equalintensity line, which occurs in the topological cases of the embodimentsof FIGS. 1 through 3.

As can be seen from the embodiment of FIG. 10, the handover area 1007determined in accordance with an embodiment of the invention herein, ismuch smaller than the effective areas of the cell sectors 1001 and 1003.Thus, on average, a method according to an embodiment of the invention,which determines the handover area, is more accurate in locating acellular phone than prior art techniques that rely on locating only thecell sector.

An embodiment according to the invention also improves accuracy, onaverage, when the cellular network specifies the location of a cellularphone using time advance data, in addition to cell identifier data. FIG.11 shows a ring-sector 1101, which is used to model the estimatedlocation of a cellular phone in such a case, in accordance with anembodiment of the invention. The additional time advance data restrictsthe location of the handset to a ring sector 1101 between two givenradii 1102 and 1103 from an antenna 1104. It will be appreciated thatuse of time-advance data, or other possible data specified by a cellularnetwork, which may narrow the modeled cell area, can be usedconsistently with embodiments herein—for example by modifying the modelfor determining effective cell area. Thus, for example, in theembodiment of FIG. 11, the cell area may be modeled as a ring sector,which is possibly extended to create an effective cell area in a similarfashion to the techniques described herein. Other shapes for cell areasmay also be used in accordance with an embodiment of the invention.Regardless of the shape of the effective cell area, techniques inaccordance with an embodiment of the invention, on average, improve theaccuracy of locating a cellular phone. Using the ring sector of FIG. 11,for example, a similar rate of reduction in area may be obtained as whenfull sectors are used as above.

Those of skill in the art will appreciate that the generalizedparameters mentioned above (such as parameters R₁, R₂, R₃, R₄, α, E₁,E₂, W₁, and W₂), may be determined empirically and calibrated by fieldtrials. For example, tests may be performed in which actual locations oftest cellular phones are known, so that the actual locations can beempirically matched against the cell map to determine proper values forthe parameters. The parameters may be estimated statistically based onthe empirical results, and may be improved as test results and otherdata are accumulated over time.

In accordance with an embodiment of the invention, a system and methodfor location of cellular phones may be used as part of a trafficinformation system, such as that described in U.S. Pat. No. 6,587,781 ofFeldman et al., a summary block diagram of which is shown in theembodiment of FIG. 12. In this system, there is determined the locationof each of a plurality of mobile sensors in vehicles traveling on a roadnetwork 12, which has been analyzed to form an oriented road sectionnetwork 14. Position data 62 is collected over time from the mobilesensors, and sampled periodically by a sampler 1 for passage to anormalized travel time calculator 2. Based on the sampled data, thetravel time calculator 2 determines a mean normalized travel time valuefor each oriented road section of the network 14. A fusion and currentpicture generator 3 then uses the calculated normalized travel times, aswell as data obtained from other sensors, to generate a current pictureof traffic conditions on the road network. A predictor 4 can then usethe current picture, as well as rules from a patterns and rulesgenerator 6, to predict traffic conditions or provide other informationto a service engine 5, which may serve a variety of applications 7. Thefusion and current picture generator 3 may fuse data from a variety ofsources, including the normalized travel time calculator 2, traffic datafrom fixed sensors 60, traffic data from traffic reports 64, and trafficdata from other sources 66.

In accordance with an embodiment of the invention, an apparatus forimplementing the technique of locating cellular phones, describedherein, can be used to generate traffic data using cellular phonelocations from phones in vehicles. For example, when a handover area isdetermined for given cellular phone, a traffic system can use thegeographical area corresponding to the handover area that has beendetermined, as an estimate of the location of a vehicle in which thatcellular phone was located at the time that handover event occurred.Based on the resulting position and time data for a large number of suchvehicles, and traffic data from other sources, a normalized travel timecalculator 2, or other traffic system component, can generate a pictureof traffic conditions for a variety of uses, including for predictingupcoming traffic conditions. In one embodiment, a technique inaccordance with those described herein for geographically locating acellular phone is implemented by the sampler module 1 of the embodimentof FIG. 12. The sampler module 1 is fed position data 62, which mayinclude streaming data relating to cellular handover events, from acellular network. The position data 62 may include, for example, cellidentifier and time advance data from a cellular carrier; as well asvehicle position data from a variety of other mobile sensor sources,such as GPS data or other Floating Vehicle Data. Vehicle position data62 from each different type of mobile sensor source is sampled by itsown adjusted sampler sub-module (included in sampler module 1 of FIG.12). Multiple sampler sub-modules may also be used for processingdifferent types of data from the same mobile sensor source. For example,separate sampler sub-modules may be used for processing cellularhandover data and cellular location server data.

FIG. 13 is a block diagram of an apparatus for locating cellular phones,in accordance with 10 an embodiment of the invention. This may be used,for example, in the traffic information system of the embodiment of FIG.12. As summarized in the block diagram of the embodiment of FIG. 13,such an apparatus 1305 for locating cellular phones may include aneffective cell-area module 1301 for determining cell-areas; a penumbraarea module 1302 for determining the penumbra area around the line ofequal intensity; and a handover area module 1303 for 15 determining thehandover area. The apparatus 1305 for locating cellular phones may beimplemented in a variety of different forms of hardware, as will beapparent to those of skill in the art upon reading the techniquesdisclosed herein. For example, the apparatus 1305 may comprise acomputer processor or specialized signal processing circuit, whichreceives data 1300 on cellular handover events, or other cellular data,generated by a cellular network; and which transmits a resultingcalculated handover area to a location-based application 1304; forexample, the traffic information system of the embodiment of FIG. 12.Various method steps described in embodiments herein may be implementedas routines in computer program code running on a computer processor1305, or as equivalent specialized circuits for data processing.

Also, an apparatus according to an embodiment of the invention need notbe implemented in the form of the embodiment of FIG. 13. For example,two possible ways of implementing techniques herein are as follows(these examples are not intended to be limiting). In a first example, acell-map of a cellular carrier may be available to a system according tothe invention. In this case, handover areas for all possiblecombinations of neighboring cells can be determined, based on thecellular map, in an off-line process, and stored in a databaseaccessible by a system according to the invention. When cellular datastreams into the system, the system uses the cell identifiers and/ortime advance data; or other cellular network data for a given handoverevent to consult the database (for example, using a lookup table) andthereby obtain the relevant handover area. Thus, in the first example,the functions of apparatus 1305 are performed off-line, and data 1300 issubsequently processed online with reference to the handover datacreated offline by module 1303. By contrast, in a second example, acell-map is not available to a system according to the invention.Instead, the system receives the geographical parameters of the cellsinvolved in each handover event, and calculates the handover areasonline based on the data stream, using, for example, the embodiment ofFIG. 13. The modules 1301-1303 of the embodiment of FIG. 13 need not bemapped directly onto different software modules; instead, the softwaremay have a different or more complex architecture implementingequivalent functionality, as will be appreciated by those of skill inthe art.

A skilled reader will appreciate that, while the foregoing has describedwhat is considered to be the best mode and where appropriate other modesof performing the invention, the invention should not be limited tospecific apparatus configurations or method steps disclosed in thisdescription of the preferred embodiment. For example, while variousembodiments herein refer to geographically locating a “cellular phone,”it will be appreciated that this term should be construed broadly torefer not only to mobile cellular handsets, but also, for example, toother modules in communication with a cellular network, such asvehicle-bound probes which communicate with a cellular network. Thoseskilled in the art will also recognize that the invention has a broadrange of applications. For example, embodiments according to theinvention for geographically locating a cellular phone may be used in awide variety of applications; including (but not limited to):location-based services, generally; traffic information systems; foremergency purposes, such as in locating a cellular phone that was usedto call an emergency number; for escape planning; and for security,intelligence, and national defense applications. It will also beappreciated that the embodiments admit of a wide range of modificationswithout departing from the inventive concepts.

What is claimed is:
 1. A method of monitoring vehicle traffic flow bydetermining successive locations of a plurality of cellular phoneslocated in a plurality of vehicles, the method comprising: repeatedlydetermining the location of at least some of the plurality of cellularphones; and sampling the locations of the at least some of the cellularphones to determine a present picture of vehicle traffic flow; whereindetermining the location of a cellular phone of the plurality comprisesdetermining the area in which handover from a first cell to a secondcell occurs, the determination of the area in which handover occursbeing based on: modeling at least a portion of a cell reception area ofsaid first cell and said second cell; and defining the area in whichhandover occurs to comprise overlapping portions of said first andsecond cell areas.
 2. The method according to claim 1, furthercomprising predicting future vehicle traffic conditions based on thepresent picture of traffic flow.
 3. The method according to claim 1,wherein the determination of the area in which handover occurs is madeby consulting a database of pre-determined handover areas for cellpairs, using handover data from a cellular network.
 4. A The methodaccording to claim 3, wherein the handover data comprises cellidentifier data.
 5. The method according to claim 3, wherein thehandover data comprises time advance data.
 6. The method according toclaim 1, wherein the determination of the area in which handover occursis made online using streaming handover data from a cellular network. 7.An apparatus for monitoring vehicle traffic flow by determiningsuccessive locations of a plurality of cellular phones located in aplurality of vehicles, the apparatus comprising: a handover area modulefor defining a handover area comprising overlapping portions of amodeled cell reception area of at least a portion of each of a firstcell and a second cell of a cellular network; and a sampler module forsampling a set of repeated location determinations of at least some ofthe plurality of cellular phones, to determine a present picture ofvehicle traffic flow, wherein each such location determination is basedat least in part on the handover area defined by the handover areamodule for a given cellular phone moving between a given first cell andsecond cell of the cellular network.
 8. The apparatus according to claim7, further comprising: a predictor module for predicting future trafficconditions based on the present picture of traffic flow.
 9. Theapparatus according to claim 7, further comprising: a handover areadatabase comprising pre-determined handover areas for cell pairs. 10.The apparatus according to claim 9, wherein the handover area module iscapable of consulting the handover area database using streaminghandover data from the cellular network.
 11. The apparatus according toclaim 10, wherein the handover data comprises cell identifier data. 12.The apparatus according to claim 10, wherein the handover data comprisestime advance data.
 13. The apparatus according to claim 7, wherein thehandover area module is capable of determining the handover area onlinebased on streaming handover data from the cellular network.